1. Field of the Invention
The present invention relates to an optical fiber draw tower, and more particularly, to a cooler of an optical fiber draw tower.
2. Description of the Related Art
In general, optical fibers are obtained by drawing a preform for optical fibers using an optical fiber draw tower. A general optical fiber draw tower includes a melting furnace for melting a preform at a high temperature to draw out uncoated optical fiber, a diameter measuring unit installed below the melting furnace for continuously measuring the outer diameter of the uncoated optical fiber to uniformly control the outer diameter of the uncoated optical fiber, a cooling unit below the diameter measuring unit, for cooling down the temperature of the uncoated optical fiber to room temperature, a coating unit below the cooling unit, for coating the surface of the uncoated optical fiber with UV-curable resin such as acryl resin or silicon resin so as to protect the uncoated optical fiber from the elements of nature, a curing unit below the coating unit, for curing the coated optical fiber, a capstan below the curing unit, for drawing out an optical fiber from the preform in a lower direction, and a spool next to the capstan, for winding the drawn optical fiber.
A method for preparing (drawing) an optical fiber coated with the UV-curable resin will be described. The preform is slowly provided into the melting furnace according to the position control mechanism of a preform position controller (not shown). Here, the preform is heated in the melting furnace to several thousands of degrees centigrade, typically, to 2,100.about.2,200.degree. C. As a result, the uncoated optical fiber is drawn from the preform. Here, the drawing force originates from the capstan and is applied to the uncoated optical fiber.
Then, the diameter measuring unit measures the outer diameter of the uncoated optical fiber drawn to determine whether the diameter is equal to a predetermined diameter, e.g., 125 pm, and sends the measured diameter values to a diameter controller (not shown). The diameter controller controls the rotating speed of the capstan such that the diameter of the uncoated optical fiber is maintained at 125 pm. Then, the capstan rotates to control the drawing force on the uncoated optical fiber in response to the control of the diameter controller, thereby drawing out the uncoated optical fiber in a downward direction.
Then, in order to protect the uncoated optical fiber cooled at high speed by the cooling unit, the coating unit coats the surface of the descending uncoated optical fiber with a UV-curable resin, e.g., acryl resin or silicon resin. Then, the optical fiber coated with the UV-curable resin is cured by the curing unit, and is then wound around the spool under the control of drawing force of the capstan.
Also, if the preform is large, the height of the optical fiber draw tower must be increased. This is because very rapid drawing is necessary as the preform becomes large. After the preform is melted passing through a melting furnace and then drawn out, the drawn optical fiber is subjected to coating. Here, prior to coating of the optical fiber, the temperature of the uncoated optical fiber it must be lowered to a predetermined temperature. In general, the temperature of the uncoated optical fiber drawn right from the melting furnace is 2,000.degree. C. or more, However, in order to guarantee stable coating on the drawn optical fiber, the temperature of the uncoated optical fiber must be cooled to at least 40.degree. C. or less (usually to room temperature). For this purpose, the temperature of the uncoated optical fiber is cooled rapidly using a cooler. However, coolers in use are not sufficient to cool the uncoated optical fiber to keep pace with the rapid drawing speed. In the cooler having a pipe shape, the drawn optical fiber is cooled by filling the pipe with helium (He).
Thus, it is necessary to increase the height of the optical fiber draw tower in order to quickly cool the uncoated optical fiber in response to the rapid drawing speed of the optical fiber, However, making the optical fiber draw tower high increases the manufacturing cost and it is not efficient. What is needed is an efficient cooler not requiring a high optical fiber draw tower.